This invention relates to a reconstructible network and, in particular, to an ATM network allowing logical reconstruction by modifying the capacity of a virtual connection.
A conventional reconstructible network of the type is described, for example, in an article entitled "Implementation Performance Evaluation for Self-sizing Network Operation" written by Yuka KATO and three others and contributed to Technical Report of IEICE (Institute of Electronics, Information and Communication Engineers), SSE-95-122 (December, 1995), pp. 37-42. As described in the KATO et al. article, the reconstructible network is aimed at reassigning physical network resources to meet variation in traffic load upon virtual paths in an ATM network in order to assure network performance.
In an asynchronous transfer mode (abbreviated ATM), a fixed-length block called a cell is used as a unit in multiplexing and exchange for a physical link. The cell contains an identifier indicative of virtual connection through which information is to be transferred. The virtual connection includes a virtual path (VP) and a virtual channel (VC). Within the cell, the identifier for the virtual connection is partly assigned to the virtual path and partly assigned to the virtual channel. As a result, a particular virtual path accommodates a plurality of virtual channels. A particular physical link accommodates a plurality of virtual paths.
Referring to FIG. 1, a conventional reconstructible network comprises a plurality of virtual channels (VC's) 1, a plurality of virtual channel handlers (VCH's) 2 (2-1 through 2-6 in the figure), a plurality of virtual paths (VP's) 3 (3-1 through 3-3 in the figure), a plurality of virtual path handlers (VPH's) 4 (4-1 through 4-4 in the figure), a plurality of physical links 5 (5-1 through 5-3 in the figure) accommodating the virtual paths 3, and a network managing system (NMS) 6.
The virtual channel handlers 2 terminate the virtual paths 3 and make the virtual paths 3 accommodate the virtual channels 1 in response to accommodation requests. Such accommodation requests (for example, telephone calls) are randomly produced so that the accommodation of the virtual channels 1 into the virtual paths 3 may not completely be successful. The probability of unsuccessfulness is used as a measure for the performance of the virtual paths 3. A product of the frequency of production of the accommodation requests and the required accommodation time is called a traffic.
The virtual path handlers 4 terminate the virtual paths 3 and make the physical links 5 accommodate the virtual paths 3. The virtual paths 3 are handled as channel groups comprising a plurality of channels such as telephone channels. The accommodation of the virtual paths 3 into the physical links 5 are definitely carried out.
The virtual channels 1 and the virtual paths 3 are collectively called the virtual connection while the virtual channel handlers 2 and the virtual path handlers 4 are collectively called communication nodes.
Supplied with a capacity setting request message from the network managing system 6, each of the virtual channel handlers 2 and the virtual path handlers 4 modifies a capacity managing table. In addition, each of the virtual channel handlers 2 terminating the virtual paths 3 modifies a traffic shaper to adjust a cell flow in each virtual path 3 and, after completion of the modification, returns a capacity setting response message. Supplied with a traffic/performance information request message, the virtual channel handler 2 returns a traffic/performance response message to the network managing system 6. Thus, the network managing system 6 controls and manages the virtual channel handlers 2 and the virtual path handlers 4 by the use of the messages transmitted and received in a polling fashion.
The virtual channel handlers 2 and the virtual path handlers 4 as the communication nodes are respectively assigned with node numbers which can be uniquely identified within the network. The physical links 5 connected to one of the communication nodes are assigned with port numbers which can be uniquely identified within the communication node in consideration. Therefore, a particular one of the physical links 5 downward from a particular one of the communication nodes can be uniquely identified within the network with reference to a combination of a specific node number and a specific port number. Such combination of the specific node number and the specific port number will hereafter be called a physical link number.
In order to reassign network resources from those virtual paths having spare capacity to those virtual paths requiring additional capacity, the network managing system 6 periodically collects traffic/performance information from the virtual channel handlers 2 to evaluate the performance, calculates VP capacity required for each VP path, and sets the capacity in each of the virtual path handlers 4 and the virtual channel handlers 2. To this end, the network managing system 6 is connected to all of the virtual channel handlers 2 and the virtual path handlers 4 within the network through managing virtual channels.
Referring to FIG. 2, the network managing system 6 comprises a database (DB) section 10, a control section 11, and a message transmit/receive section 12.
The database section 10 comprises a traffic database 101, a topology database 102, and a routing list database 103.
As illustrated in FIG. 3A, the traffic database 101 holds a traffic information table storing traffic and performance information related to the traffic and the performance of each virtual path 3 within the network and collected from each virtual channel handler 2. Specifically, the traffic information table comprises first through fourth entries indicative of a VP number, traffic information, performance information, and a VP capacity, respectively. The VP number comprises a set of a node number, a port number, and a VP identifier uniquely identified by the port number. Thus, the VP number is uniquely identified within the network.
As illustrated in FIG. 3B, the topology database 102 holds a topology information table indicative of the state of connection of the virtual channel handlers 2 and the virtual path handlers 4 as well as idle capacity of the physical links 5 connecting the virtual channel handlers 2 and the virtual path handlers 4. Specifically, the topology information table comprises first through third entries indicative of the physical link number of an adjacent node, the node number, and the idle capacity.
As illustrated in FIG. 3C, the routing list database 103 holds a routing list table indicative of a routing list comprising a sequence of the physical link numbers of those physical links through which each virtual path 3 within the network passes. Specifically, the routing list table comprises first and second entries indicative of the VP number and the physical link number.
The control section 11 comprises a capacity managing unit 111, a performance managing unit 112, a capacity calculating unit 113, a capacity setting unit 114, and a reduction candidate selecting unit 115.
The performance managing unit 112 periodically collects in a polling fashion the traffic and the performance information of a virtual channel 1 accommodated in a virtual path 3 terminated by a particular virtual channel handler 2 in consideration, and renews the traffic database 101. In response to a request from the capacity managing unit 111, the performance managing unit 112 acquires from the traffic database 101 the performance information of the virtual path 3 and evaluates whether or not the performance is satisfactory.
The capacity calculating unit 113 acquires from the traffic database 101 the traffic information and the performance information of the virtual path 3 specified by the capacity managing unit 111, calculates the required capacity for the virtual path 3, and, if necessary, renews the VP capacity in the traffic database 101.
The capacity setting unit 114 successively delivers capacity setting request messages to all of the virtual path handlers 4 and the virtual channel handlers 2 designated in the routing list for the virtual path 3 specified by the capacity managing unit 111 to carry out capacity setting operation. When capacity setting response messages are sent from all of the virtual path handlers 4 and the virtual channel handlers 15 in consideration, the capacity setting unit 114 renews the VP capacity in the traffic database 101 and the idle capacity in the topology database 102 for all of the physical links 5 present in the route of the virtual path 3.
The reduction candidate selecting unit 115 refers to the routing list database 103 and searches another virtual path 3 accommodated in the physical link common to an expansion-candidate virtual path 3 with its routing list specified. If it is found, the routing list for such another virtual path 3 is extracted.
The capacity managing unit 111 carries out judgement and execution of expansion or reduction of the VP capacity by the use of the performance managing unit 112, the capacity calculating unit 113, the capacity setting unit 114, and the reduction candidate selecting unit 115.
The message transmit/receive section 12 comprises a message transmitter 121 and a message receiver 122.
The message transmit/receive section 12 is connected through managing virtual channels to all of the virtual channel handlers 2 and the virtual path handlers 4.
The message transmitter 121 transmits the request messages to the virtual channel handlers 2 and the virtual path handlers 4. The message receiver 122 receives the response messages from the virtual channel handlers 2 and the virtual path handlers 4.
Referring to FIG. 4, operation of the network managing system 6 in FIG. 2 will be described.
In a step A1, the capacity managing unit 111 makes the performance managing unit 112 judge, with reference to the traffic database 101, whether or not performance requirement is satisfied for a particular virtual path 3. If it is satisfied, the operation comes to an end.
If the performance requirement is not satisfied, the step A1 proceeds to a step A2. In the step A2, the capacity managing unit 111 makes the capacity calculating unit 113 calculate, as a new VP capacity, the required VP capacity for the particular virtual path 3 as an expansion candidate. A difference between the new VP capacity thus calculated and a current capacity is obtained as a requested expansion value.
The step A2 is followed by a step A3. In the step A3, the capacity managing unit 111 makes the capacity setting unit 114 refer to the topology database 102 and examine whether or not each of the physical links 5 on the route of the virtual path 3 can be expanded because it has the idle capacity sufficient to satisfy the requested expansion value calculated in the step A2. If expansion is possible, the step A3 proceeds to a step A10.
If the expansion is impossible, the step A3 proceeds to a step A4. In the step A4, the capacity managing unit 111 makes the reduction candidate selecting unit 115 select as a reduction candidate virtual path another virtual path 3 passing through the physical link 5 common to the expansion candidate virtual path to obtain the VP number of the reduction candidate virtual path and the physical link number of the physical link 5 used in common. If no reduction candidate virtual path is selected, the operation comes to an end.
If any reduction candidate virtual path is selected, the step A4 proceeds to a step A5 in which the capacity managing unit 111 makes the capacity calculating unit 113 calculate as a new capacity the required VP capacity for each reduction candidate virtual path 3.
The step A5 is followed by a step A6. In the step A6, calculation is made of the difference between the new capacity thus calculated and the current capacity for each reduction candidate virtual path. Specifically, the current capacity is subtracted from the new capacity to obtain the difference. If the difference has a minus value, the reduction in capacity is allowable. Based on this knowledge, judgement is made about whether or not any virtual path 3 can be reduced in capacity. If no virtual path 3 can be reduced in capacity, expansion in capacity of the expansion candidate virtual path is impossible and the operation comes to an end.
If any virtual path 3 is reducible in capacity, the step A6 proceeds to a step A7. In the step A7, the capacity managing unit 111 makes the capacity calculating unit 113 calculate, with reference to the difference in VP capacity calculated in the step A6, the physical link number of the physical link 5 used in common by the reduction candidate virtual path and the expansion candidate virtual path, and with reference to the routing list of the expansion candidate virtual path 3, the total sum of newly available capacity in each physical link on the route of the expansion candidate virtual path. The newly available capacity results from reduction in capacity of the reduction candidate virtual path. The minimum total sum is used as an allowable expansion value for the VP capacity. A smaller one of the allowable expansion value and the requested expansion value calculated in the step A2 is selected as an expandable value. This operation prevents the expansion over the requested expansion value.
Then, the step A7 is followed by a step A8 in which examination is made about whether or not the expansion is possible because the expandable value is not equal to zero. If it is not possible, the operation comes to an end.
If the expandable value is not equal to zero and the expansion is possible, the step A8 proceeds to a step A9. In the step A9, the capacity managing unit 111 makes the capacity setting unit 114 modify the capacity of each of the capacity-reducible virtual paths 3 into the new capacity calculated in the step A5. The step A9 is followed by a step A10.
In the step A10, the capacity managing unit 111 makes the capacity setting unit 114 set a new capacity which is a total sum of the expandable value calculated in the step A7 and the current capacity.
Now, operation of the prior art in FIG. 1 will be described.
The capacity managing unit 111 in a reconstructible server 7 (not shown in FIG. 1) makes the performance managing unit 112 evaluate whether or not the performance of the virtual path 3-1 is satisfactory (step A1). Since the performance is not satisfactory, expansion of the capacity is desired. However, no idle capacity is present in the physical links 5-1 and 5-2 in the route of the virtual path 3-1. In this state, expansion is impossible. Therefore, the capacity managing unit 111 makes the reduction candidate selecting unit 115 select the other virtual paths 3-2 and 3-3 sharing the physical links 5-1 and 5-2 with the virtual path 3-1, respectively. Then, the capacity managing unit 111 makes the capacity calculating unit 113 calculate the required capacity for each of the virtual paths 3-2 and 3-3 (step A5).
As a result, the virtual paths 3-2 and 3-3 are judged reducible so that the capacity of each of the physical links 5-1 and 5-2 becomes available. A smaller value of the available capacity is selected as an expansion value for the virtual path 3-1 (step A7).
Then, the capacity managing unit 111 instructs the virtual channel handler 2-2, the virtual path handlers 4-1, 4-4, and 4-2, and the virtual channel handler 2-3 to reduce the virtual path 3-2. Likewise, the capacity managing unit 111 instructs the virtual channel handler 2-4, the virtual path handlers 4-2, 4-4, and 4-3, and the virtual channel handler 2-5 to reduce the virtual path 3-3 (step A9).
Finally, the capacity managing unit 111 instructs the virtual channel handlers 2-1 and 2-6 to expand the virtual path 3-1 (step A10).
The conventional reconstructible network described above is disadvantageous in that the performance can not be assured following rapid variation in traffic.
As described above, the network managing system exclusively and successively executes all those steps required in capacity reassignment, including performance management, capacity calculation, capacity setting, and reduction candidate selection.
In addition, a series of these steps are executed retrieving and renewing the databases storing various information for the whole network, including the information related to connection between the physical links and the communication nodes and the idle capacity of the physical links, the information of the physical links in the route of the virtual connection, and the information related to the traffic and the performance.
Thus, it takes a long time to complete capacity expansion for the virtual connection whose performance is not satisfactory.